1. Technical Field
The present invention relates to an electromagnetic fuel injector (injection valve) for an internal combustion engine.
2. Background Art
There has been conventionally used an electromagnetic fuel injector which is driven in response to an electric signal output from an engine control unit in an internal combustion engine for an automobile or the like.
This type of fuel injector is configured such that an electromagnetic coil and a yoke are arranged around a hollow cylindrical fixed core. And a nozzle body containing a movable element (thereafter call “needle”) with a valve element is fixed to the lower portion of the yoke, so that the needle is urged toward a valve seat by the force of a return spring.
A two-point support guide system is generally used for the needle in order to achieve the stability of a stroke movement. For example, as disclosed in Japanese Patent Laid-Open No. Hei 11-200993, in the case where the movable element is a needle valve, the tip of the needle valve is slidably guided on the inner circumference of a fuel swirler housed inside a nozzle body. And as to another point, a large-diameter portion functioning as a guide surface on a movable side is formed in the needle valve, to be thus slidably guided on the inner circumference of the nozzle body. A similar two-point support guide system is used for a needle configured by integrally coupling a ball and a rod which serve as a valve element.
In recent years, a fuel injector for directly injecting fuel into a cylinder in an internal combustion engine has been put to practical use also in a gasoline engine.
In the direct injection type of fuel injector, there has been proposed a long nozzle injector in which a nozzle body disposed under a yoke is slenderly elongated. In fixing such a long nozzle injector to a cylinder head, only the slender nozzle body occupying little space is placed on the cylinder head. And in the injector, a large-diameter body consisting of a yoke, a connector mold and the like can be provided apart from other parts and the cylinder head without any interference. Therefore, in the case where parts such as a suction valve and a intake manifold are densely disposed in the vicinity of the cylinder head, said fixing of the long nozzle injector has advantage of the high degree of fixing freedom.
In the above-described two-point support guide system for the needle, it is necessary to finish (grind) a guide hole formed at the inner circumference of the nozzle body in the case where the stroke movement of the needle is guided on the inner circumference of the nozzle body. If the nozzle body is elongated, the guide surface is deeply positioned, thereby making machining difficult. In the meanwhile, even in the case where the guide surface is formed at the inner circumference near an opening of the nozzle body, followed by finishing, the inner circumference of the nozzle body requires a high grinding accuracy, thereby increasing a fabricating cost accordingly. Consequently, cost reduction is desired.
In addition, since the valve element collides with a valve seat during a valve closing operation in the electromagnetic fuel injector, the valve is accidentally opened by a bounce of the valve element, thereby inducing a fear of so-called secondary injection. Therefore, there are various demands for the technique for preventing such secondary injection, the configuration which contributes to assembling facilitation, in particular, automatic assembling, and the like.